You shouldn’t have to corn cob blast unless it is black and/or moldy if it is new construction. You should first clean any rough spots by sanding, apply a borate treatment since it can only be applied when the wood is bare. To stain first or chink first is your preference on which look you would like. If it is a small log (6”) I would recommend caulking with Energy seal and then stain. If they are bigger logs 8” or larger I would stain and then use Perma Chink.